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tag: v2.6.39-rc5
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/*
* Functions related to interrupt-poll handling in the block layer. This
* is similar to NAPI for network devices.
*/
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/bio.h>
#include <linux/blkdev.h>
#include <linux/interrupt.h>
#include <linux/cpu.h>
#include <linux/blk-iopoll.h>
#include <linux/delay.h>

#include "blk.h"

int blk_iopoll_enabled = 1;
EXPORT_SYMBOL(blk_iopoll_enabled);

static unsigned int blk_iopoll_budget __read_mostly = 256;

static DEFINE_PER_CPU(struct list_head, blk_cpu_iopoll);

/**
* blk_iopoll_sched - Schedule a run of the iopoll handler
* @iop: The parent iopoll structure
*
* Description:
* Add this blk_iopoll structure to the pending poll list and trigger the
* raise of the blk iopoll softirq. The driver must already have gotten a
* successful return from blk_iopoll_sched_prep() before calling this.
**/
void blk_iopoll_sched(struct blk_iopoll *iop)
{
unsigned long flags;

local_irq_save(flags);
list_add_tail(&iop->list, &__get_cpu_var(blk_cpu_iopoll));
__raise_softirq_irqoff(BLOCK_IOPOLL_SOFTIRQ);
local_irq_restore(flags);
}
EXPORT_SYMBOL(blk_iopoll_sched);

/**
* __blk_iopoll_complete - Mark this @iop as un-polled again
* @iop: The parent iopoll structure
*
* Description:
* See blk_iopoll_complete(). This function must be called with interrupts
* disabled.
**/
void __blk_iopoll_complete(struct blk_iopoll *iop)
{
list_del(&iop->list);
smp_mb__before_clear_bit();
clear_bit_unlock(IOPOLL_F_SCHED, &iop->state);
}
EXPORT_SYMBOL(__blk_iopoll_complete);

/**
* blk_iopoll_complete - Mark this @iop as un-polled again
* @iop: The parent iopoll structure
*
* Description:
* If a driver consumes less than the assigned budget in its run of the
* iopoll handler, it'll end the polled mode by calling this function. The
* iopoll handler will not be invoked again before blk_iopoll_sched_prep()
* is called.
**/
void blk_iopoll_complete(struct blk_iopoll *iopoll)
{
unsigned long flags;

local_irq_save(flags);
__blk_iopoll_complete(iopoll);
local_irq_restore(flags);
}
EXPORT_SYMBOL(blk_iopoll_complete);

static void blk_iopoll_softirq(struct softirq_action *h)
{
struct list_head *list = &__get_cpu_var(blk_cpu_iopoll);
int rearm = 0, budget = blk_iopoll_budget;
unsigned long start_time = jiffies;

local_irq_disable();

while (!list_empty(list)) {
struct blk_iopoll *iop;
int work, weight;

/*
* If softirq window is exhausted then punt.
*/
if (budget <= 0 || time_after(jiffies, start_time)) {
rearm = 1;
break;
}

local_irq_enable();

/* Even though interrupts have been re-enabled, this
* access is safe because interrupts can only add new
* entries to the tail of this list, and only ->poll()
* calls can remove this head entry from the list.
*/
iop = list_entry(list->next, struct blk_iopoll, list);

weight = iop->weight;
work = 0;
if (test_bit(IOPOLL_F_SCHED, &iop->state))
work = iop->poll(iop, weight);

budget -= work;

local_irq_disable();

/*
* Drivers must not modify the iopoll state, if they
* consume their assigned weight (or more, some drivers can't
* easily just stop processing, they have to complete an
* entire mask of commands).In such cases this code
* still "owns" the iopoll instance and therefore can
* move the instance around on the list at-will.
*/
if (work >= weight) {
if (blk_iopoll_disable_pending(iop))
__blk_iopoll_complete(iop);
else
list_move_tail(&iop->list, list);
}
}

if (rearm)
__raise_softirq_irqoff(BLOCK_IOPOLL_SOFTIRQ);

local_irq_enable();
}

/**
* blk_iopoll_disable - Disable iopoll on this @iop
* @iop: The parent iopoll structure
*
* Description:
* Disable io polling and wait for any pending callbacks to have completed.
**/
void blk_iopoll_disable(struct blk_iopoll *iop)
{
set_bit(IOPOLL_F_DISABLE, &iop->state);
while (test_and_set_bit(IOPOLL_F_SCHED, &iop->state))
msleep(1);
clear_bit(IOPOLL_F_DISABLE, &iop->state);
}
EXPORT_SYMBOL(blk_iopoll_disable);

/**
* blk_iopoll_enable - Enable iopoll on this @iop
* @iop: The parent iopoll structure
*
* Description:
* Enable iopoll on this @iop. Note that the handler run will not be
* scheduled, it will only mark it as active.
**/
void blk_iopoll_enable(struct blk_iopoll *iop)
{
BUG_ON(!test_bit(IOPOLL_F_SCHED, &iop->state));
smp_mb__before_clear_bit();
clear_bit_unlock(IOPOLL_F_SCHED, &iop->state);
}
EXPORT_SYMBOL(blk_iopoll_enable);

/**
* blk_iopoll_init - Initialize this @iop
* @iop: The parent iopoll structure
* @weight: The default weight (or command completion budget)
* @poll_fn: The handler to invoke
*
* Description:
* Initialize this blk_iopoll structure. Before being actively used, the
* driver must call blk_iopoll_enable().
**/
void blk_iopoll_init(struct blk_iopoll *iop, int weight, blk_iopoll_fn *poll_fn)
{
memset(iop, 0, sizeof(*iop));
INIT_LIST_HEAD(&iop->list);
iop->weight = weight;
iop->poll = poll_fn;
set_bit(IOPOLL_F_SCHED, &iop->state);
}
EXPORT_SYMBOL(blk_iopoll_init);

static int __cpuinit blk_iopoll_cpu_notify(struct notifier_block *self,
unsigned long action, void *hcpu)
{
/*
* If a CPU goes away, splice its entries to the current CPU
* and trigger a run of the softirq
*/
if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
int cpu = (unsigned long) hcpu;

local_irq_disable();
list_splice_init(&per_cpu(blk_cpu_iopoll, cpu),
&__get_cpu_var(blk_cpu_iopoll));
__raise_softirq_irqoff(BLOCK_IOPOLL_SOFTIRQ);
local_irq_enable();
}

return NOTIFY_OK;
}

static struct notifier_block __cpuinitdata blk_iopoll_cpu_notifier = {
.notifier_call = blk_iopoll_cpu_notify,
};

static __init int blk_iopoll_setup(void)
{
int i;

for_each_possible_cpu(i)
INIT_LIST_HEAD(&per_cpu(blk_cpu_iopoll, i));

open_softirq(BLOCK_IOPOLL_SOFTIRQ, blk_iopoll_softirq);
register_hotcpu_notifier(&blk_iopoll_cpu_notifier);
return 0;
}
subsys_initcall(blk_iopoll_setup);
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